Strength and microstructure of friction stir welded additively manufactured Scalmalloy® in as-welded and heat-treated conditions

This study investigates the feasibility of butt friction stir welding of LPBF additively manufactured FSW Scalmalloy® plates, assessing the microstructural and mechanical properties of the joints in as-welded and heat-treated conditions. The heat treatment consisted of age hardening to benefit from the strengthening effect of Al-Sc precipitates on the FSW joint strength. The influence of the build direction of the additive layers on joint microstructure and mechanical performances has also been determined. The results show that the build direction of the Scalmalloy® plates affects neither the FSW process nor the microstructural and mechanical properties of the welded joints. The FSW thoroughly modifies the microstructures of the as-printed Scalmalloy®, eliminating the intrinsic porosity associated with the AM process. The heat input in the welding process causes the precipitation of Al-Sc phases so that the following aging heat treatment has a limited effect on improving joint strength. Although the Al-Sc strengthening enhances the strength and hardness of Scalmalloy®, there is a significant loss of ductility (from 16 % to 4 %), as also pointed out by the absence of plastic deformation on the surface fracture of the heat-treated tensile samples.